If A and B are two square matrices such that B=−A−1BA then A+B2=
0
A2+B2
A2+2AB+B2
A+B
B=A−1BA⇒AB=−AA−1BA =−BA(A+B)2=(A+B)(A+B) =A(A+B)+B(A+B)=A2+AB+BA+B2=A2+B2